1. Field of the Invention
The present invention relates to a paper feeding apparatus which holds sheet-like recording media, and which successively feeds the recording media to an image forming section, and an image forming apparatus which includes the paper feeding apparatus.
2. Description of the Related Art
In an image forming apparatus such as a copying machine, printer or facsimile apparatus, when sheet-like recording media for printing images thereon, such as paper or OHP film, are used in large quantities, a paper feeding apparatus is employed which holds the plurality of recording media beforehand so as to feed them in succession.
The paper feeding apparatus comprises an apparatus body and a recording paper case. The recording paper case is detachable from the apparatus body in order to replenish the recording paper.
FIGS. 7A and 7B are schematic views showing the conveyance mechanism of a paper feeding apparatus 100. FIG. 7A is a plan view, while FIG. 7B is a side sectional view. The paper feeding apparatus 100 comprises an apparatus body 101, and a recording paper case 102. The apparatus body 101 has pickup rollers 103, an upper guide 104, a lower guide 105, a conveyance roller 106, and a pinch roller 107. The recording paper case 102 has separation pawls 108, a push-up plate 109, and a spring 110. Incidentally, only components relevant to the conveyance mechanism in the paper feeding apparatus 100 are shown in FIGS. 7A and 7B. Besides, the upper guide 104, the conveyance roller 106, and the pinch roller 107 are omitted from FIG. 7A in order to facilitate understanding of the shape of the lower guide 105. Sheets of recording paper 200 are put on the push-up plate 109 included in the recording paper case 102, and the push-up plate 109 is pushed upwards by the spring 110. Owing to the upward push of the push-up plate 109, the corner parts of the uppermost recording paper 201 are pushed against the separation pawls 108.
In feeding the recording paper, the pickup rollers 103 included in the apparatus body 101 are rotated to carry out the uppermost recording paper 201 in a conveyance direction indicated by an arrow B. On this occasion, a frictional force acts between the uppermost recording paper 201 and the second uppermost recording paper, so that the second uppermost recording paper is about to move in the same direction as that of the uppermost recording paper. However, the movement is hampered by the separation pawls 108, and only the uppermost recording paper 201 is separated and carried to a guide section. A conveyance path is changed to be upward by the upper guide 104 and the lower guide 105. The recording paper 201, carried out by the rotations of the pickup rollers 103, is bent along the conveyance path, and the front end edge thereof reaches the conveyance roller 106 and the pinch roller 107. The conveyance roller 106 and the pinch roller 107 hold the front end part of the recording paper 201 therebetween, and carry out this recording paper to the conveyance path leading to an image forming section.
The reduction of an installation area is required of the image forming apparatus as the desire of users, and reduction in the size of the apparatus is a requisite for incarnating the desire. Accordingly, the conveyance path needs to be shortened to the utmost in a horizontal direction, and it must be abruptly changed as shown in FIG. 7B. Even when the path change is abrupt, recording paper is easily caused to follow up the path change in a case where guides exist before and behind the change part of the path, and where the recording paper moves along the path of comparatively small cross section. However, in a case as in the paper feeding apparatus 100 where the recording paper is conveyed from that peripheral space of the recording paper case 102 in which the movement of the recording paper is not constrained, to the path which is surrounded with the upper guide 104 and the lower guide 105, and where the path change is abrupt, drawbacks such as the bending and jamming of the recording paper occur at the change part of the path. When the corner parts of the front end of the recording paper touch the lower guide 105, the movement of the front end part of the recording paper is sometimes hampered by load resistance such as a frictional force which the recording paper receives from the lower guide 105. On this occasion, the rear part of the recording paper is further carried out by the pickup rollers 103, so that the corner parts of the front end of the recording paper are bent. Moreover, when the bent parts hitch on the guide or any other part to make the recording paper immobile, the paper jamming takes place.
According to a paper feeding apparatus stated in Japanese Unexamined Utility Model Publication JP-U 1-75050 (1989), an upper guide plate is shaped into a trapezoid whose upside is this side as viewed in a paper feed direction, and whose downside is the opposite side. Thus, recording paper is conveyed while its corner parts curled upwards are being broadened, so that the occurrence of the bending, jamming, etc. of the recording paper is relieved.
FIGS. 8A and 8B are views showing a state where the recording paper 200 is separated by the separation pawls 108. Although the middle part of the uppermost recording paper 201 is moved in the conveyance direction by the rotations of the pickup rollers 103, each corner part 201a of the recording paper has its movement limited by the separation pawl 108 and is flexed as shown in FIG. 8A. When the middle part of the recording paper 201 is further moved in the conveyance direction, the corner part 201a thereof is released from the separation pawl 108. The corner part 201a, however, remains flexed to continue a state where it is deformed downwards as shown in FIG. 8B. The corner part 201a deformed in this manner is more susceptible to the load resistance of the guide and to undergo the drawback. With the lapse of time, the corner part 201a is about to resume the original state where it is not deformed. However, when the conveyance speed of the recording paper 201 is raised in order to heighten the processing speed of the image forming apparatus, the deformed corner part 201a comes into touch with the lower guide 105 before resuming the original state, and the problem of the prior art, namely, the drawback of the paper jamming ascribable to the bending of the front end part of the recording paper becomes liable to occur. Besides, the paper feeding apparatus stated in JP-UM-A-1-75050 cannot attain the advantage in the case where the path has changed abruptly, or in the case where the corner part has been deformed downwards as in the deformation ascribable to the pawl separation.